1. Field of the Invention
The present invention relates to a vehicle-use power generation control apparatus and a vehicle-use power generation control system.
2. Description of Related Art
Recent vehicles have lower idle speeds and lower engine frictions to improve fuel efficiency, and accordingly, torque variation caused when a vehicle accessory starts operation affects engine rotational speed more substantially. As a technique to stabilize rotational speed of a vehicle engine in the idle state, it is known to perform so-called gradual excitation control in order to restrict power generation increase rate of a vehicle generator when the vehicle engine idles, to thereby prevent the generator torque from rapidly increasing. The voltage of a vehicle battery charged by the vehicle generator falls substantially when the vehicle generator is applied with a large electrical load while the gradual excitation control is in operation. Accordingly, if the vehicle battery is in an over-discharged condition, or in a condition where its internal resistance is excessively large, or in a condition where its terminal is loosely connected, the operating voltage of vehicle-mounted equipment supplied with electricity from the vehicle battery may drop as low as 10 V. In this case, the vehicle mounted equipment including an engine control unit may malfunction or may suffer system fail.
To deal with this disadvantage, there is known a technique in which the gradual excitation control is inhibited when the power generation voltage (the output voltage of the vehicle generator) falls below a predetermined voltage in order to restore the power generation voltage to its normal level. For example, refer to Japanese Patent Application Laid-Open No. H9-107640.
However, the above technique has a problem in that when the power generation voltage falls below the predetermined voltage, and accordingly the gradual excitation control is inhibited, since the generator torque rapidly increases, the vehicle engine may be stalled if its piston displacement is not sufficiently large.
Further, the above technique has a problem in that since the gradual excitation control (power generation restriction control) is inhibited when the power generation voltage falls below the predetermined voltage, if the power generation voltage rises and falls around this predetermined voltage at frequent intervals, the gradual excitation control is inhibited and resumed at frequent intervals. In this case, the engine rotational speed is likely to fluctuate widely, and it may become difficult or may be late to recover the operating voltage of the vehicle mounted equipment which has fallen due to the fall of the power supply voltage. The rotational speed of a vehicle generator driven by a vehicle engine varies coincidentally with engine ignition timing, and the power generation voltage of the vehicle generator varies along with the variation of the rotational speed. Accordingly, if the power generation voltage comes close to a threshold to determine inhibition of the gradual excitation control, the power generation voltage rises and falls around the threshold at frequent intervals causing the above problem.